Directional air flow pilot valves may serve a variety of useful purposes in connection with a gas turbine aircraft turbine engine, such as to control the engaging and disengaging of an aircraft engine's thrust reverser. In general, aircraft turbine engine thrust is directed towards the rear of the plane. Upon landing, in an effort to diminish lift as well as slow the aircraft, the direction of thrust may partially be reversed with the use of a thrust reverser. The developer of the present inventions, Honeywell International, Inc., has for years successfully designed, developed, and manufactured turbine engines that have directional pilot valves used in connection with thrust reversers.
Aircraft air flow pilot valves are generally known and reliable devices used in the operation of aircraft control systems. Directional air flow pilot valves are valves that permit air flow in a specific direction. One type, known as a directional pilot valve (DPV), has a sealing rod assembly, which is moved along the longitudinal axis of the DPV in and out of the valve housing assembly. Actuated movement of the sealing rod assembly is commonly referred to as stroking. The outer limit of movement is commonly known as maximum stroke length. Generally speaking, the flow rate of air through the DPV will change as the stroke of the valve is increased or decreased, because the valve is opened and/or closed by the linear motion of the sealing rod.
Proper calibration of the DPV helps to ensure proper operation of the thrust reverser. As initially manufactured, a DPV will operate to control passage of air through the valve assembly at a known rate. Over time, due to internal wear, debris and foreign matter which may enter the valve unintentionally, and other factors, the flow rate of the directional valve may significantly change. Such a change in flow rate may result in the operation of the DPV outside of the desired calibration range. However, as flight control systems are redundant, conventional gas turbine engines and thrust reversers are operationally safe and reliable despite the foregoing variations in calibration of a DPV.
In operation, a DPV may have two general forces acting upon it—the first is a constant physical load force applied against the opening of the valve and the second is an air pressure force applied in a direction opposite to the physical load force. To test a DPV for proper calibration, it is desirable to therefore apply forces in an opposing manner to simulate the valve's operational response. To calibrate the valve, these forces are applied in a known and controlled fashion while the stroke of the valve is varied. In general, such a calibration test can measure the effective air pressure and leakage when the DPV is in a seated position, as in closed, and the volume of air flow when the DPV is in an open position.
At present, a technician performing a calibration measurement test upon a DPV attempts to physically hold, apply force and measure pressure and flow rate—a physically demanding and complex process that may result in inaccurate measurement. If a DPV cannot be properly calibrated, the entire DPV is replaced with a new valve or remanufactured to original specifications to ensure proper operation.
The replacement with a new valve is wasteful of resources and costly. The one alternative is to remanufacture the valve. However, remanufacturing is a complex process involving specialized tooling, training and a time-consuming assembly and test processes. With either replacement or remanufacture, the flow rate calibration is based upon the design specification and not the actual flow rates of the given valve. Thus, even with new replacement or remanufacture there is a possibility of a calibration that is inaccurate to some degree
Hence, there is a need for an improved DPV calibration system with improved characteristics to overcome one or more of the drawbacks identified above. The present invention satisfies one or more of these needs.